Like all other games in the 3D Universe, there are small blinking lights visible in the night sky, and occasionally during the day. These move much faster than any other vehicle available in the game.
In GTA Liberty City Stories, it is likely that the lights were intended to look like airplanes. If the player uses mods to get close enough, they can find that they are just non-solid spheres. In the game files they are called "UFOLIGHTS".